Typically, a so-called HST (Hydro Static Transmission) is mounted in a work vehicle such as a wheel loader. A HST type of work vehicle drives a hydraulic pump using an engine and drives a movement hydraulic motor using hydraulic fluid which is discharged from the hydraulic pump. Due to this, the work vehicle moves. In such an HST type of work vehicle, it is possible to control vehicle speed and traction force by controlling the rotation speed of the engine, the displacement of the hydraulic pump, the displacement of the movement hydraulic motor, and the like.
As disclosed in Japanese Laid-open Patent Application Publication No. 2011-052794, the displacement of the hydraulic pump is controlled using a pump displacement control cylinder. The pump displacement control cylinder controls the displacement of the hydraulic pump according to pressure of hydraulic fluid which is supplied to the pump displacement control cylinder (referred to below as “pump pilot pressure”). In the work vehicle which is disclosed in Japanese Laid-open Patent Application Publication No. 2011-052794, the pressure of the hydraulic fluid from a charge pump is supplied to the pump displacement control cylinder by adjusting an engine sensing valve (a speed sensing valve). The hydraulic fluid which is discharged from the charge pump is supplied to a pilot port of the engine sensing valve. The charge pump is a fixed displacement pump which is driven using the engine. As a result, the engine sensing valve changes the pump pilot pressure according to the rotation speed of the engine.
On the other hand, the work vehicle is provided with a forward and backward progression operation member and a forward and backward progression switching valve. The forward and backward progression operation member is operated by an operator in order to switch forward and backward progression of the vehicle. The forward and backward progression switching valve switches the supply direction of the hydraulic fluid to the pump displacement control cylinder. A controller switches the supply direction of the hydraulic fluid to the pump displacement control cylinder using the forward and backward progression switching valve when switching between forward and backward progression using the forward and backward progression operation member is detected. Due to this, the discharge direction of the hydraulic fluid from the hydraulic pump is switched; and as a result, the progression direction of the vehicle is switched from forward progression to backward progression or from backward progression to forward progression.